Insert and blank for a wind turbine blade root

ABSTRACT

A composite material blank comprising an elongate blank body extending between a first end face and a second end face; said blank body extending in a longitudinal direction, parallel to a longitudinal axis thereof, and having four peripheral sides; each said first and second end face having edges which define a trapezoid shape; wherein the peripheral sides of said blank body connect the edges of said first end face with the edges of said second end face; and wherein said first trapezoid end face is inverted in relation to said second trapezoid end face. A method of manufacturing a composite blank, and a wind turbine blade root insert which may be formed from a blank.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/770,116, filed Jun. 5, 2020 (pending), which is a U.S. National Phaseapplication of PCT Application No. PCT/DK2018/050334, filed Dec. 7, 2018(expired), which claimed priority to U.S. Provisional Application No.62/596,260 filed Dec. 8, 2017 and Danish Application No. PA2018 70017,filed Jan. 11, 2018, the disclosures of which are incorporated byreference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to an insert for a wind turbine bladeroot, a method of manufacturing such an insert, a blank in a method ofmanufacturing inserts for a wind turbine blade root, and a method ofmanufacturing such a blank.

BACKGROUND OF THE INVENTION

US2011044817 relates to a process for manufacturing a blade connectionof a rotor blade for a wind energy system which comprises fasteningelements for fastening the blade connection to a hub. The fasteningelements are provided on a circular arc, preferably equidistant fromeach other, and spaced from each other with wedge-shaped spacerelements.

A wind turbine blade for a large horizontal axis wind turbine may havesignificant mass, perhaps in the region of 10 tonnes or more, up to 30tonnes or more. Blades are fastened to a hub to make up a rotor. A rotorrotates on a main shaft to drive a generator. Blades are attached attheir root end to a hub flange. A blade is typically connected to a hubflange using a group of bolts. The stresses on a blade hub connectionare considerable, owing chiefly to blade mass and wind force, as well asthe effect of perpetual rotation of the rotor, which tends to vary thedegree and direction of the forces on the blade with every rotation ofthe rotor. Vibrations in the system can also be considerable. With anexpected lifetime of 20 years and more, the fatigue performance of theblade hub connection is critical. A bolt group, often known as studbolts, may be connected to the blade root using threaded bushings,embedded into the root end of a blade. Such bushings are usuallycylindrical, often made of steel. The bushings transfer the loads fromthe blade to the stud bolts. The stud bolts transfer those loads to thehub, which is a rigid, often cast, component. Considering the fatiguerequirements placed on a blade hub connection, the manner of embeddingbushings into a blade root can be critical. The present inventionaddresses the design of an insert, into which a bushing may be embedded,and methods of preparing the same. The insert, generally made fromcomposite material and containing a bushing, may be embedded in a bladeroot along with other inserts. The blade root, with its inserts, therebypresents a connection face for a bolted connection to a hub.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a composite material blank in amethod of manufacturing a pair of inserts for a wind turbine blade root,the blank comprising an elongate blank body extending between a firstend face and a second end face. The blank body extends in a longitudinaldirection, parallel to a longitudinal axis thereof, and has fourperipheral sides; each said first and second end face having edges whichdefine a trapezoid shape; wherein the peripheral sides of said blankbody connect the edges of said first end face with the edges of saidsecond end face and wherein said first trapezoid end face is inverted inrelation to said second trapezoid end face. By inverted is meant thatthe second end face is turned through 180 degrees in relation to thefirst end face. The blank may thereby exhibit two opposing, parallel,planar faces and two non-parallel side faces. The side faces may benon-planar or partially planar. The blank may be shaped such that it maybe bisected into two equal parts by a single plane. In other words, theblank may preferably be shaped to generate two identically dimensionedparts, when bisected along a plane transverse, and preferablyperpendicular to the blank's lengthwise axis. Preferably, the blank is acomposite material blank in a method for manufacturing two wind turbineblade root inserts simultaneously. Therefore, the blank may preferablycomprise a first and a second wind turbine blade root bushing. A bushingmay be cylindrical. A cylindrical bushing may extend about alongitudinal axis parallel with or coincident with the longitudinal axisof said blank. A bushing may be a metal bushing, preferably a steelbushing. A bushing may preferably comprise an attachment region forengagement of the bushing with a wind turbine hub connection element. Abushing attachment region may comprise a bore. A bore may include athreaded portion. A wind turbine hub connection element may comprise astud bolt. A stud bolt may be attachable to a bushing by engagement of athreaded portion of the stud bolt with a threaded portion of a bushingbore. Preferably the first and second bushings are arranged inopposition to each other in the blank.

The blank may comprise a first end portion and a second end portion. Inparticular, said blank body may comprise a first end portion and asecond end portion. Preferably, a first bushing may be embedded in afirst end portion of a said blank, while a second bushing may beembedded in a second end portion of said blank. Therefore, the blank maycomprise first and second end portions each having a respective bushing.In embodiments, along said first and second end portions, in a lengthdirection of said blank, the four peripheral sides of said blank bodymay all be planar and extend parallel to the longitudinal axis of saidblank body. The blank body may have a generally quadrilateral crosssection along all or part of its length. The blank may further include atransition portion in which said side faces of said blank body are notparallel to said longitudinal axis. In embodiments, the blank body mayextend along a transition portion, between said first end portion andsaid second end portion. A bisection of the blank may generate two windturbine blade root inserts of equal dimensions.

At each end portion the peripheral faces of said elongate blank body mayinclude a major face, a minor face and a pair of side faces, the majorface being wider than the minor face. The blank body may be an elongatequadrilateral shape resembling a prism. The blank body may have a topsurface and an opposing bottom surface which are generally planar. Theblank body top and bottom surfaces may preferably be generally parallel.

As mentioned, the first aspect of the invention provides an intermediateproduct, or blank. The blank can be cut into two, to generate twoinserts. When laid in side-by side abutment in a blade mould, theinserts preferably describe a circular section, preferably withoutrequiring an additional wedge-shaped spacer element.

Preferably the blank body portion comprises two end portions separatedby a transition portion. The transition portion may exhibit a pair ofside faces. Each side face of said transition portion may meet a sideface of the respective first and second end portions. Each side face maybe non-planar. Preferably, each side face may be predominantly planarand marginally non-planar. In embodiments, each side face of thetransition portion may comprise two or more substantially planar facets.Alternatively, each side face of the transition portion may be curved.

The blank preferably has rotational symmetry of order 2. The blank maybe cut in half along a diagonal line to form a pair of matching inserts.

The two respective bushings may be embedded into a blank. The bushingsmay be cylindrical. A bushing may be embedded into each end region ofsaid blank. A bushing may protrude slightly from an end face of saidblank. Typically the bushings may be separated by a longitudinal,cylindrical core. A core may be non-metallic and may be fibrous forexample or made from a bulk material such as foam or balsa. Optionallythe blank may further comprise two or more fibrous battens surroundingthe bushings and the core. Each batten may have a deltoid cross-section.The battens may thereby give the elongate blank a generallyquadrilateral cross-section.

The side faces may be slightly curved. More preferably, they may bepartly planar, preferably so that the inserts generated therefrom mayform a continuous ring when the planar side faces of adjacent insertsare laid side-by-side, in contact with each other.

In one embodiment the cross-section of each end portion of the blank hasa pair of straight, opposing, parallel faces and a pair of opposingsides which are nearly parallel but which lie on slightly convergentplanes. More preferably the cross section of each end portion of theblank is a trapezoidal cross-section.

Optionally each end portion of the blank has a prismatic shape. In thiscase the cross-section of each end portion does not vary along alongitudinal axis of the blank. Preferably, a transition portion betweenthe end portions of the blank may have a cross-section which variesalong the longitudinal axis of the blank. Preferably, a cross section ofthe transition portion may be generally quadrilateral, although in someembodiments, the side faces in particular may be slightly concave.

The invention also provides a method of manufacturing a pair of insertsfor a wind turbine blade root, the method comprising: producing a blankaccording to the first aspect of the invention; and cutting the blankinto two equal pieces by making a diagonal cut through the blank body.In embodiments, a diagonal cut may be made through the transitionportion. In embodiments, a diagonal cut through the blank may beentirely in the transition portion. The diagonal cut may define a planewhich passes transversely across opposing parallel faces of the blankbody, and which passes diagonally across opposing side faces of saidblank body.

The invention also provides a method of manufacturing the blank, themethod comprising; placing an assembly in an infusion mould; injecting amatrix material into the infusion mould so that the matrix materialinfuses the assembly; curing the matrix material; and after the matrixmaterial has cured, removing the blank from the infusion mould.

In one example the infusion mould comprises first and second mould partswhich meet at a split line; wherein each of said first and second mouldparts respectively moulds two principal surfaces of said blank; whereinsaid first mould part moulds one of two opposing side faces of saidblank and one of two opposing parallel faces of said blank, while saidsecond mould part moulds the other of said two opposing side faces ofsaid blank and the other of said two opposing parallel faces of saidblank. Optionally, each mould part may mould a portion of each end faceof said blank. Preferably the mould split describes a diagonal planethrough the generally quadrilateral cross-section of said blank body.This arrangement may be called a diagonal split mould. This diagonalsplit mould arrangement enables the cured blank to be removed easilyfrom the mould.

Typically the assembly may be formed by fitting the bushings to oppositeends of a core, and fitting two or more fibrous battens around thebushings and the core. Each batten may have a deltoid cross-section sothat the battens give the blank assembly a quadrilateral cross-section(typically rectangular or trapezoid), and the matrix material infusesthe fibrous battens in the infusion mould.

A further aspect of the invention provides an insert for a wind turbineblade root, the insert comprising: an end portion comprising a bushingwith a threaded bore, wherein the end portion has peripheral faces whichform a cross-section, the peripheral faces including a major face, aminor face and a pair of side faces, the major face being wider than theminor face; and an extension portion which extends away from the endportion to a tip; wherein the extension portion has an outer face whichmeets the major face of the end portion, an inner face which meets theminor face of the end portion, a pair of side faces which meet the sidefaces of the end portion, and a height between its inner and outer faceswhich reduces as it extends away from the end portion, wherein a widthof the outer face reduces as the extension portion extends away from theend portion. The blank generated by a method according to thisdisclosure may be generally prismatic and may have a predominantlyquadrilateral cross-section. Therefore, the extent of the narrowing ofan insert away from its end portion may be in the order of just a fewmillimetres from the end portion to a tip of the extension portion;possibly just one or two millimetres. Possibly three or fourmillimetres.

Cutting the blank into two parts typically produces a pair of equal,matching inserts according to the further aspect of the invention. Theinsert has a height and a width which both taper inwardly towards thetip.

The height may reduce in a series of steps or in another non-uniformway, but more preferably it reduces uniformly as the extension portionextends away from the end portion.

The inner face is preferably planar. This enables the inner face to beformed easily, for example by cutting the blank with a cutting implementsuch as rotary saw.

Each side face of the extension portion may comprise one or moresubstantially planar facets. Alternatively, each side face of theextension portion may be curved.

The side faces of the end portion of an insert may be curved, but morepreferably they may be planar so that multiple inserts, when arrangedside-by-side, form a continuous ring with the planar side faces ofadjacent inserts in contact with each other.

The parallel, opposing major and minor faces of the end portion maypreferably be planar and preferably flat.

Preferably an end portion of the insert has a polygonal cross-sectionwith substantially straight sides—for instance it may have a trapezoidcross-section with four substantially straight sides. Alternatively, thecross-section of the end portion of the insert may have one or morecurved sides.

In one embodiment the cross-section of the end portion of the insert hasa pair of straight sides which are nearly parallel but which areslightly convergent.

Optionally an end portion of the insert has a prismatic shape in whichall sides are parallel to the blank longitudinal axis. In this case thecross-section of each end portion does not vary along a longitudinalaxis of the blank. By contrast, a transition portion of said blank mayhave an almost prismatic shape, in other words a transition portion mayhave a cross-section which varies along the longitudinal axis of theinsert.

A further aspect of the invention provides a wind turbine bladecomprising: a root and a tip, the wind turbine blade extending from theroot to the tip; and a plurality of inserts according to the furtheraspect of the invention embedded in the root.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying drawings, in which:

FIG. 1 shows a wind turbine;

FIG. 2 shows a blade of the wind turbine of FIG. 1;

FIG. 3 shows a root end of the blade of FIG. 2;

FIG. 4 is an enlarged end view of part of the root end of FIG. 3;

FIG. 5 shows a wind turbine blade root insert;

FIG. 6a is a cross-sectional view along the length of a double-endedspindle assembly, wrapped with a transition layer;

FIG. 6b is a cross-sectional view through the assembly of FIG. 6,sectioned along a line y-y and additionally showing lay-up elementsaround the transition layer;

FIG. 6c shows a sectional profile across the grooves of a bushing, witha series of shallow and sinuous crests and troughs;

FIG. 7 is a schematic side view of a bushing wrapped in a transitionlayer and showing connecting sections of filamentary material betweenadjacent grooves;

FIG. 8 is a sectional side view showing two grooves and a transitionlayer covering the grooves;

FIG. 9 is a sectional side view showing two grooves and an alternativetransition layer covering the grooves;

FIG. 10 is a sectional side view showing two grooves and a furtheralternative transition layer covering the grooves;

FIG. 11a shows a filamentary material being wound onto a spindle to forma set of windings over a material wrapping layer;

FIG. 11b shows fibrous sheet material being wrapped around a spindle;

FIG. 12 shows filamentary material being wound a blank assembly, tosecure its elements in place;

FIG. 13 is a figurative isometric view showing pultruded battens fittedaround one of the bushings;

FIG. 14 shows an alternative arrangement in which the battens are formedfrom glass rods;

FIG. 15 shows an alternative batten formed from glass rods of varyingcross section;

FIG. 16 shows an infusion moulding arrangement;

FIG. 17 is an isometric view of a blank;

FIG. 18 is a side view of the blank of FIG. 17;

FIG. 19 is a plan view of the blank of FIG. 17;

FIG. 20 is a bottom view of the blank of FIG. 17;

FIG. 21 is a cross-sectional view of the second end portion of the blankof FIG. 17;

FIG. 22 is a cross-sectional view half way along the blank of FIG. 17;

FIG. 23 is a cross-sectional view of the first end portion of the blankof FIG. 17;

FIG. 24 is a plan view of an insert cut from the blank of FIG. 17;

FIG. 25 is a bottom view of the insert of FIG. 24;

FIG. 26 is a side view of the insert of FIG. 24;

FIG. 27 shows a diagonally split, infusion mould arrangement;

FIG. 28 shows a cross-section through a first lobed batten arrangement;

FIG. 29 shows a cross-section through a second lobed batten arrangement;

FIG. 30 shows a diagonal cross-sectional view of one end of a blankincluding an embedded bushing;

FIG. 31 is an isometric view of an end cap;

FIG. 32 shows a blank;

FIG. 33 shows an isometric view showing the outer profile of a blankwith an alternative geometry.

DETAILED DESCRIPTION OF EMBODIMENT(S)

FIG. 1 shows a horizontal axis wind turbine 10. The wind turbine 10comprises a tower 12 supporting a nacelle 14 to which a rotor 16 ismounted. The rotor 16 comprises a plurality of wind turbine blades 18that extend radially from a central hub 19. In this example, the rotor16 comprises three blades 18.

FIG. 2 is a view of one of the blades 18. The blade 18 extends from agenerally circular root 20 to a tip 22 in a longitudinal ‘spanwise’direction, and between a leading edge 24 and a trailing edge 26 in atransverse ‘chordwise’ direction. The blade 18 comprises a shell 27which may be formed primarily of fibre-reinforced plastic (FRP). Theblade 18 comprises a suction surface 28 and a pressure surface 29. Thesuction and pressure surfaces define a thickness dimension of the blade.

The blade 18 transitions from a circular profile to an airfoil profilemoving from the root 20 of the blade 18 towards a shoulder 25 of theblade 18, which is the widest part of the blade 18 where the blade hasits maximum chord. The blade 18 has an airfoil profile of progressivelydecreasing thickness in an outboard portion of the blade 18, whichextends from the shoulder 25 to the tip 22 of the blade 18.

FIG. 3 shows the root 20 of one of the blades 18, and FIG. 4 is an endview of a sector of the root 20. The root 20 is preferably attached tothe hub 19 by stud-bolts (not shown) which may extend from or through ahub flange (not shown) into metal bushings 40, four of which are shownin FIG. 4. Each bushing extends in a longitudinal direction and has aninternal axial bore 109. Each steel bushing 40 may be embedded in aninsert 105 shown in FIG. 5. The insert 105 has an insert body 108 inwhich the bushing 40 is embedded. The inserts 105 may have aquadrilateral, preferably trapezoidal, cross section and may be laidside by side in a ring around the circumference of the root 20. Theinserts 105 may be embedded between walls 41 and 42. These walls 41 and42 may in particular be of glass fibre reinforced composite material. Inthe illustrated embodiment, composite wall 41 forms an outside layer ofthe shell 27 at the blade root 20 while composite wall 42 forms aninside layer of the shell 27 at the root 20. The inserts 105 may beplaced in a mould and then integrated with the blade shell 27 through aresin infusion moulding process such as vacuum infusion. To achievethis, the inserts 105 may be pre-manufactured and laid into the mould bypositioning them on lay-up material for the shell 27. Additional lay-upmaterial may be applied over the inserts 105 in the mould, prior toinfusion.

Note that in embodiments, the side faces 143 of the inserts 105 arepreferably planar so that the inserts 105 can be arranged, as shown inFIG. 4, in a continuous ring with the planar side faces 143 of adjacentinserts 105 in abutting contact with each other. If the inserts 105 havea slightly trapezoidal shape, then the respective side faces 143 may bearranged side-by-side to form a circular arrangement as illustrated inFIGS. 3 and 4, without requiring wedge-shaped spacers between them.

Aspects of a preferred method of manufacturing a matching pair of theinserts 105 are shown in FIGS. 6a to 16. First, a double-ended spindle167 may be set up, onto which a transition layer 102 may be made up.Advantageously, two bushings 40 may be longitudinally spaced at eitherend of a longitudinal core 62 to form the spindle 167. The illustratedspindle 167 comprises a core 62 with frustoconical ends 63, and a pairof steel bushings 40 which each have frustoconical recesses 65 intowhich the ends 63 of the core may be push-fitted as shown in FIG. 6a .The core 62 may be made from a variety of materials, such aspolyethylene terephthalate (PET) foam, pultruded glass, glass-fibrereinforced composite material, or wood.

With reference to FIG. 30, a bushing 40 may serve both to transfer loadsbetween a hub connection element, such as a stud bolt (not shown), andthe bushing 40, as well as to transfer loads between the bushing 40 andthe insert body 108, the insert 105 being embedded in a wind turbineblade root 20. For transferring loads between a hub connection elementand the bushing 40, the bushing may be provided with an internal bore109, the internal bore 109 in turn having an engagement element 66 forengagement with a hub connection element (not shown). In the caseillustrated, the bushing 40 may have an internal thread 66 forengagement with a stud bolt (not shown), for connection to a windturbine hub. In addition, the bushing 40 may have a textured externalsurface (see grooves 68) for improving load transfer between the bushing40 and the insert body 108. In FIG. 30, the textured outer surface 68 ofthe bushing 40 extends axially adjacent the engagement element 66. Thismay serve to maximise the area available on the bushing 40 surface forload transfer to the insert body 108. In other words, the two loadtransfer arrangements at the bushing 40 may be axially coincident. Inorder to improve the performance of a bushing 40, it may be desirable toaxially separate those areas which perform the respective load transferfunctions. Such an axial separation may reduce local peak loads in thebushing 40 and is illustrated by way of example in FIG. 6a .Accordingly, a bushing 40 may include an end region 61 which terminatesin a planar end face 61 a at a root end of the bushing, and a bodyregion 59 which extends from the end region 61 to the opposite end ofthe bushing. The end region 61 may be non-textured, i.e., it may have apredominantly smooth outer surface. By smooth is meant predominantlycylindrical, and preferably without external surface features. A smoothsurface may be roughened for better adhesion to resin, although suchroughening may not be regarded as a surface feature in this context. Abody region 59 may be provided with a textured outer surface forengagement between the bushing 40 and the insert body 108. In such anarrangement, with the textured outer surface of the body portion 59axially offset from the smooth, cylindrical outer surface of the rootend region 61, the load transfer between the bushing 40 and the insertbody 108 may be localised away from the root end region 61. Inembodiments, an internal thread 66 or stud bolt engagement element, maybe positioned in a root end region 61 of a bushing 40. In this way, asillustrated in FIG. 6a , load transfer between a hub connection elementand the bushing 40, via engagement element 66, may be axially separatedfrom load transfer between the bushing and the insert body 108. This mayreduce peak loads experienced by the bushing 40. In embodiments, theroot end region 61, axially offset from the body region 59, may exhibita larger minimum outer diameter than the minimum outer diameter of theend region 61. This arrangement may ensure that, in embodiments where athread 66 is axially offset from a textured region of a bushing 40, thenthe bushing 40 has a greater wall thickness in the region of the thread66 than in the region of the textured outer surface. This, in turn, mayimprove the ability of the bushing 40 to withstand high levels of stressthrough the engagement element 66, perhaps especially at momentary highlevels of stress.

Optionally therefore, the internal thread 66 in a bore 109 through thebushing 40 may be arranged within the end region 61. The end region 61may have a smooth (un-grooved) or grooved cylindrical outer surface. Theend region 61, offset from the body region 59 may be configured so thatso that none of the grooves 68 encircle the internal thread 66.Offsetting the grooves 68 from the thread 66 in this way maximizes thewall thickness of the end region 61, making it crack-resistant. It alsoseparates the bushing 40 into two, axially spaced, functional regions:the end region 61 and the body region 59. The end region 61 transmitsloads between the stud bolt and the bushing 40, while the body region 59transmits loads between the bushing 40 and the insert body 108, via atransition layer 102.

An effective wall thickness h (FIG. 6a ) of the bushing 40 may varybetween a maximum, measured between the very outer extent of the bushing40 e.g., at its root end region 61 or at a crest 69 between adjacentgrooves and the inner wall of a bore 109, and a minimum extent betweenthe grooves of an internal thread 66 and the grooves 68 of an undulatingprofile. A greater minimum wall thickness h at the threaded bore makesthe area of high load transfer at an end region 61 morestress-resistant.

FIG. 7 is a side view showing three grooves 68 at a bushing 40 surface.FIG. 8 is a sectional view showing two of the grooves 68. As shown mostclearly in FIG. 7, the grooves 68 and ridges 69 are annular rather thanhelical, so they each lie perpendicular to the length of the spindle167, i.e., perpendicular to the axial direction of the bushing 40.

After a spindle 167 has been set up, a transition layer 102 may be builtup around it as shown in FIG. 8. The transition layer 102 may comprisefibrous plies 98, each overlaid with a respective associated set ofwindings 80. In the illustrated example in FIG. 8, the transition layer102 may comprise four fibrous plies 98, each overlaid with a respectiveassociated one of four sets of windings 80. In FIG. 8, the four fibrousplies 98 are individually numbered 81-84, the ply 81 being the innermostply. The number of fibrous plies 98 may however be two or three or fouror five or more. Each ply 98 preferably has its own associated set ofwindings 80. In FIG. 8, The four sets of windings 80 are individuallynumbered 85-88, the innermost set of windings 85 being associated withthe innermost ply 81. The transition layer 102 may be a continuous layerwhich terminates at each end of the spindle 167. In embodiments, thetransition layer 102 may terminate where a last groove 68 meets the endregion 61 of a bushing 40, as shown in FIG. 6a . Alternatively, arespective transition layer 102 may be applied such that it surrounds arespective bushing 40 at either end of said spindle 167.

The plies 98 may comprise sheets of fibrous sheet material 164, onesheet 164 being shown in FIG. 11b . By way of example the fibrous sheetmaterial 164 may comprise glass fibre or synthetic material fibre suchas high tensile polymeric material fibre. The term fibrous is used herealthough it may include fibrous sheets made of filamentary material suchas glassfibre or other extruded type continuous filamentary material.The fibrous sheet material 164 may be selected from combinations of oneor more of: unidirectional sheets, biaxial sheets (e.g., +45°/−45°) ortri-axial sheets (e.g., +45°/0°/−45°). By way of example, the fibroussheet material 164 may be a nonwoven fabric made with unidirectionalfibre layers stacked in different orientations and held together bythrough-thickness stitching. In embodiments, the fibrous sheet material164 of an outer ply 98 may have a higher basis weight (g/sm) than thefibrous sheet material 164 of an inner ply 98. In a typicalconstruction, the fibrous sheets 164 which make up the plies 98 may havea basis weight between approximately 400 g/sm and 1600 g/sm. By way ofexample, in one preferred embodiment, the first (innermost) ply 81 maycomprise fibrous sheet material 164 in the form of a 600 gram per squaremeter (g/sm) biaxial sheet (+45°/−45°), while one or more of the otherplies 98 may comprise fibrous sheet material 164 in the form of biaxialsheets (+10°/−10°) with a higher weight, such as for example 1200 g/sm.Alternatively, some or all of the plies 98 may be made up of multiplesheets—for example the first (innermost) ply 81 may comprise two sheetswith each sheet having a basis weight of 300 g/sm.

FIGS. 11a, 11b and 12 show a tool for forming the transition layer 102.The spindle 167 is rotatably mounted between a pair of bearings 130.First, as indicated in FIG. 11b , an innermost fibrous ply 81 is woundonto the spindle 167 by unwinding it from a spool 136 of fibrous sheetmaterial 164 and rotating the spindle 167 by at least one complete turn.In embodiments, two or more complete turns may be preferred so that theinnermost ply 81 is formed from multiple layers of the fibrous sheetmaterial 164 forming a spiral. Initially the ply 81 has a cylindricalprofile as shown in FIG. 11b and covers the grooves 68 and the core 62.After wrapping a length of the fibrous sheet material 164 around thespindle 167, the sheet material 164 may be cut, leaving the spindle 167completely wrapped by at least one turn of the fibrous sheet material164.

Next, as shown in FIG. 11a , the spindle 167 is rotated while a line offilamentary material 131 such as filamentary tow is fed from a spool132. A typical filamentary material used for this purpose may be e.g.,carbon fibre or glassfibre or high-tensile polymeric material. Examplesinclude 12K carbon fibre tow. “12K” denotes the fact that thefilamentary material 131 is a bundle of 12,000 filaments, although othergauges of tow may be used such as e.g., anywhere between 2K and 40K.Initially the spool 132 may be positioned in line with a first groove 68at or near an end of the bushing 40. For example, the spool 132 mayinitially be positioned at or nearby an end region 61 of the bushing 40.Thereafter, the spindle 167 is rotated so that the filamentary material131 is wound into a first groove forming a winding 80 around theinnermost ply 81 and binding that portion of the ply 11 into a groove 68of the bushing. The number of turns of the spindle 167 at this stagedetermines the number of windings 80 of filamentary material 131 in thegroove 68. For example, one or two or three or four or more turns of thespindle 167 may be made, generating correspondingly one or two or threeor four or more windings 80 in the groove 68. Preferably, the spool 132may be moved along a track 134 until the filamentary material 131 is inline with a next groove 68. The spindle 167 continues to be rotated asthe spool 132 of filamentary material 131 moves incrementally betweenthe adjacent grooves 68, so that an angled connecting section 70 of thefilamentary material 131 rides over the ridges 69 between the grooves 68as shown in FIG. 7 and connects together windings 80 in adjacent grooves68. The process then continues groove-by-groove 68 until a first set ofwindings 80 is in place. In FIG. 8, the first set of windings is shownwith the number 85 and has two windings per groove. The filamentarymaterial 131 is then tied off at each end, for instance by wrapping itover itself.

The illustration at FIG. 8 shows how a first set of windings 85 draws anassociated first ply 81 into the grooves 68 of the bushing 40 so that itdeforms from a cylindrical profile to adopt the wrinkled or corrugatedprofile shown in FIG. 8, including circumferential annular corrugationswhich are anchored into the grooves 68 by the first set of windings 85as shown in FIG. 8.

Next, a second fibrous ply 98, shown in FIG. 8 with numeral 82, iswrapped around the spindle 167 and a second associated set of windings80, shown in FIG. 8 with numeral 86, is wrapped around it, binding oranchoring it into the grooves 68—this time with e.g., four windings 80per groove 68 rather than the two as illustrated in FIG. 8 over theinnermost ply 81. The second set of windings 86 draws the associatedsecond ply 82 into the grooves 68 so that the ply 82 adopts theundulating or corrugated profile shown in FIG. 8, includingcircumferential annular corrugations which are anchored into the grooves68 by the windings 86. The process may be repeated to complete thetransition layer 102, for example by adding further plies 98 (shown inFIG. 8 with numerals 83 and 84) bound in place by additional associatedsets of windings 80 (shown in FIG. 8 with numerals 87 and 88).

The sets of windings 80 (shown in FIG. 8 as four sets of windings 85-88)run along the grooves 68 and alternate with the fibrous plies 98 (shownin FIG. 8 as four fibrous plies 81-84) which overlie the grooves 68. Theinnermost plies 98 may have significantly undulating profiles includingcircumferential annular corrugations which are anchored into the grooves68 by their associated windings 80. This anchoring provides a stronginterface which resists the bushing 40 being pulled out axially from thefinished insert body 108, and is fatigue resistant. The fibrous sheetmaterial 164 making up the plies 98 may be wrapped around the bushing 40in such a way as to apply a fibre direction running across the groovesat an oblique angle to the grooves 68 such as 45°. Additionally oralternatively, the fibrous sheet material 164 may be wrapped around thebushing 40 such as to apply a combination of fibre directions runningacross the grooves 68. In this way, for example, one ply 98 may exhibita fibre direction at 45° while another ply 98 may exhibit a fibredirection at 90° or 60° or 75° etc. As a result of the tightly woundfilamentary material 131 making up windings 80 around the fibrous sheets164, the plies 98 running across the grooves 68 thereby adopt acorrugated shape, or corrugations, as they are anchored into the grooves68 by the windings 80.

The corrugations progressively reduce in amplitude from ply-to-ply in adirection away from the bushing 40 surface so that the corrugations ine.g., a relatively outer ply 98 may be relatively shallow and, unlikethe first, second and third plies 98 (shown in FIG. 8 as innermost plies81-83), the corrugations of a relatively outer ply such as a fourth ply98 (shown in FIG. 8 with numeral 84) or subsequent ply 98 may hardlyextend into the grooves 68. In embodiments, the number of windings 80overlying a ply 98 may progressively increase from one ply to asubsequent ply in a radial direction away from the bushing 40 surface.In optional embodiments, the outermost fibrous ply 98 of the transitionlayer 102 (shown as ply 89 in FIG. 8) may be wrapped around an outermostcorrugated ply 80 (shown as ply 84 in FIG. 8) in such a way as tomaintain a cylindrical, un-corrugated profile because no windings 80 areapplied around it. Optionally this cylindrical outermost ply 90 mayextend to cover the end region 61 of the bushing 40, unlike thecorrugated plies 81-84.

The windings 80 may be formed by rotating the spindle 167, each rotationof the spindle 167 forming a single winding 80. The number of windings80 per groove 68 for each set of windings may increase in a radialdirection away from the bushing 40 surface. So the sets of windings 80,illustrated in FIG. 8 with numerals 85-88, may have two, four, six andeight turns per groove 68 respectively. Accordingly, the number offilaments per groove 68 may thereby correspondingly increase in a radialdirection away from the bushing 40 surface. By way of example, with twowindings 80 of a 12K filamentary tow over a given ply 98 in a singlegroove 68, there may be a 24,000 individual filament count (e.g., theinnermost, first set of windings 85 shown over innermost ply 81 in FIG.8). This may increase to e.g., 96,000 filaments per groove 68 over asubsequent or outermost ply 98 (e.g., the fourth set of windings 88 overthe fourth ply 84 shown in FIG. 8).

As mentioned above, the circumferential grooves 68 and ridges 69 arepreferably annular. The term “annular” is used herein to denote a closedor endless non-helical shape, which may or may not be circular. So theremay be multiple unconnected annular grooves 68, rather than connectedgrooves which would collectively form a single helical external threadwhich runs along the full length of the body region 59 of the bushing.The annular groove shape enables multiple windings to be wrapped intoeach groove with a single pass of the spool 132. In an alternativeembodiment, a helical external thread may be used (not illustrated), butin this case multiple passes of the spool 132 along an entire groovedbody region 59 must be used if it is required to wrap multiple windings80 into the external thread.

The outer surface of the bushing 40 has a sectional profile across thegrooves 68 and ridges 69 with a series of crests and troughs as shown inFIGS. 6a, 6c and 8. The crests and troughs may be triangular as in FIG.6a , or with flat crests as in FIG. 8, but in FIG. 6c a more preferredsinuous sectional profile is shown. In this case the sectional profilehas rounded convex crests (corresponding with the ridges 69). Therounded crests may for example have a radius of curvature of about 4-8mm, optionally 4-6 mm, optionally 4 or 5 mm, optionally about 4.54 mm.The sectional profile also has rounded concave troughs (correspondingwith the grooves 68) with a radius of curvature of about 4-8 mm,optionally 4-6 mm, optionally 4 or 5 mm, optionally about 4.54 mm. Theillustrated grooves 68 have a depth A and are separated by a pitch P. Inthe case of FIG. 6c the pitch P is 10 mm, and the depth A is 1.5 mm. Sothe grooves are relatively shallow and the ratio A/P is low—in this caseabout 1/6.7. This low ratio makes the walls of the grooves less steepwhich make it easy to anchor the fibrous plies into thegrooves—particularly the innermost ply 81 which must closely follow thesinuous profile of the bushing as shown in FIG. 8. Other values of thepitch P and depth A may be used.

FIG. 9 shows an alternative transition layer 102 a, formed usingwindings alone. In embodiments, an initial set of windings 90 offilamentary material 131 which may run at a first angle to the lengthdirection of the bushing 40. By way of example, the initial set ofwindings may be wound at a first angle of 90° to the length direction ofthe bushing 40. Further windings 91 of filamentary material 131 may bewound around the bushing 40 at a different angle, e.g., 15°, 30°, 45°,60° or 75°. In embodiments, the filamentary material windings 90, 91 maycomprise glassfibre or carbon fibre tow. FIG. 10 shows a furtheralternative transition layer 102 b also formed using windings alone. Inthe case illustrated in FIG. 10 a single set of windings 100 is arrangedover the grooves 68, at a given winding angle to the bushing 40, with noadditional overlying windings 91. By way of example the filamentarymaterial 131 of the illustrated windings 100 may be glass or carbonfibre. These may run at 90° to the length direction of the bushing 40.

In the method described above, the sheet material 164 forming each ply98 of the transition layer 102 may extend almost the full length of thespindle, up to an end region 61 of each bushing 40. In other embodiments(not shown) each ply 98 may be formed from multiple sheets laid up sideby side, or it may be formed by winding a narrow strip or tape offibrous material onto the spindle 167 thereby to cover the bushing 40and all of or part of the core 62 in a spiral.

In the example described above, the windings 80 may optionally be formedfrom filamentary material 131 in the form of tow, such as carbon tow. Inalternative embodiments, perhaps for cost reasons, the filamentarymaterial 131 may be replaced by a twisted fibrous yarn (not shown)provided the requisite level of tension can be applied to it andmaintained.

Once the transition layer 102 has been formed as described above, two ormore fibrous battens 148 may be positioned around the transition layer102 to form the insert body 108. These battens may preferably give theinsert body 108 a square or trapezoidal cross-section. A batten 148 canhave different forms. These battens may include for example: a pultrudedpreform 150 as shown in FIG. 13, or assemblies of pultruded glass fibrerods 160, 170 as shown in FIGS. 14 and 15 respectively. Note that inFIG. 13, a bushing 40 is illustrated, while the transition layer 102 isnot shown. The pultruded glassfibre rods may in particular be providedin a single gauge, as shown for example in FIG. 14 or in a mix ofgauges, as shown in FIG. 15. In all cases, the battens 148 allow togenerate a desired cross-sectional shape of the insert body 108 prior toa wrapping and/or moulding step for further forming the insert 105. Thelongitudinally arranged battens 148 also give structural strength to theinsert body 108. In embodiments the battens 148 may be porous andcapable of being infused by resin. In one embodiment (not shown) thebattens may be formed by placing lengths of rope alongside the bushing40, preferably along and adjacent to the transition layer 102.

As shown in the example of FIG. 13, the preforms 150 may have a deltoidcross-section with a concave cylindrical inner face 151. The deltoidsmay approximately conform to the convex cylindrical outer contour of atransition layer 102 (see e.g., FIG. 6b ), and a pair of outer faces 152which meet at a convex or outer corner or edge 153. In embodiments, apreform 150 may be made from pultruded, fibrous material in a resinmatrix. Alternatively, in embodiments, a preform 150 may comprise a“dry” pultruded fibre material containing binder material but no resin,so it remains porous. The “dry” fibre material may be pultruded bycoating fibres in the binder material, or by adding powdered bindermaterial to the fibre material, and then pulling them through a heateddie having the required deltoid cross-section. The binder material holdsthe fibres together so the preform 150 retains the deltoidcross-section. In the context of the deltoids, or preforms, the term“fibre” is intended to designate filamentary material such as continuousfilamentary material such as glassfibre or carbon fibre or otherextruded filamentary material such as filamentary polymeric material.

In FIG. 13 or FIG. 6b , the insert is shown having four fibrous battens148 in the form of pultruded preforms 150. Each preform 150 preferablyhas a deltoid cross-section with a concave inner face 151 which liesadjacent, and may preferably contact, the transition layer 102. Notethat for purposes of illustration, the transition layer 102 is not shownin FIG. 13, to enable the grooved outer surface of the bushing to beseen. Note also that in this example, the grooves in the outer surfaceare shown almost up to the root end of the bushing, unlike in FIG. 6a inwhich the end region 61 of the bushing has no grooves.

The pair of outer faces 152 meet at an external corner 153 of thedeltoid preform 150. Each preform 150 may have an identicalcross-section. In this way, the deltoid preforms 150 give the insertbody 108 a square cross-section. In the alternative example of FIG. 14,the insert body 108 may have only two battens 148, each shaped in theform of a half hourglass shape, having two deltoid lobes.

A plurality of pultruded rods 160 or 170 may be aggregated or assembledtogether into an approximate deltoid shape. In an embodiment, as shownin FIG. 14, pultruded rods 160 which may be of a same gauge may beaggregated to form longitudinally extending deltoid shapes. Theseaggregated rods 160 may then be laid alongside a wrapped bushing 40 togenerate an insert body 108 having the desired cross-sectional shape andhaving the desired structural properties.

In further embodiments (not shown) lengths of rope may be used to formthe battens 148 instead of pultruded preforms 150 or rods 160, 170. Suchrope may be porous. Lengths of rope may be positioned approximately asillustrated in the embodiment of FIG. 14, although it may be preferredto use a single larger gauge rope which, being compliant, may be formedinto a deltoid shape, occupying the corresponding space along a wrappedbushing 40.

The use of four separate fibrous battens 148 (as in FIG. 13) may bepreferred over two battens 148 as in FIG. 14, since they can be movedabout independently to better conform around a bushing 40 and provide a“wedging” effect which can improve consolidation in the final mouldedproduct.

FIG. 15 illustrates a further alternative deltoid fibrous batten 148, inthis case formed by an assembly of porous glass fibre rods 170 havingvarying circular cross-sectional areas so they form the required deltoidcross-section. The rods 170 can be stabilised by being attached to amesh 171 wrapped around the transition layer, or by placing them in aformer and bonding them together at discrete locations. Thecross-sections approximate to a deltoid shape, so the battens give thepart a square cross-section. According to the embodiment illustrated inFIG. 15, a large gauge pultruded rod 170 may be positioned at alongitudinally extending corner position of an insert body 108. Smallergauge pultruded rods 170 may be positioned in flank regions adjacent thecorner rod 170. In some embodiments, flanking rods may also be ofvarying gauge. Flanking rods 170 may decrease in cross sectional size ina direction away from a larger gauge corner rod 170.

An advantage of using ropes or rods 160, 170 for the battens 148,compared with the use of pultruded preforms 150, is that the ropes orrods 160, 170, being stock products, are available at low cost and donot require a bespoke pultrusion die.

The battens 148 may extend along the full length of the bushing and core62, covering not only the transition layer 102 but also the end region61 of the bushing. Alternatively, the battens 148 may terminate at theend of the body region 59 where the body region 59 meets the end region61. Accordingly, one-piece end caps (discussed below with reference toFIG. 31) may be fitted over the end regions 61, the end caps having therequired square or trapezoidal outer profile of the insert body 108.

The cylindrical profile of the outermost ply 89 of the transition layer102 ensures a smooth connection surface to interact with the deltoidbattens 148 described above. After the battens 148 have been fitted, anouter shell layer 186 (shown in FIG. 6b ) comprised of sheets of fibroussheet material 164 may be wrapped around the assembly, thereby to bindtogether the assembly of the battens 148 and the wrapped bushing 40. Theouter shell layer 186 may thereby form an outside region of the insertbody 108. The fibrous sheets 164 of the outer layer 186 may compriseunidirectional fibres or bi-axial or tri-axial fibre layers. The fibroussheet material of the outer shell layer 186 may optionally have a higherbasis weight than one or more of the plies 98 of the transition layer102 around the bushing 40. Alternatively, the fibrous sheet material ofthe outer shell layer 186 may optionally be of a same material or typeas one or more of the plies 98 of the transition layer 102 around thebushing 40. Optionally, the fibrous sheet material 164 of the outershell layer 186 may be applied by unwinding the material 164 from thespool 136 and rotating the spindle 167 by a required number of turns. Inembodiments, a single turn may be applied although it may be preferredto apply two or three or more turns of the sheet material 164 to make upthe outer shell layer 186. Finally, the outer shell layer 186 may besecured in place by winding filamentary material 131 around it, as shownin FIG. 12. The filamentary tow 131 around the outer shell layer 186 maybe the same as or of a different type than the filamentary material 131of the windings 80 over the plies 98 of the transition layer 102.Optionally, 12K carbon fibre tow may be wound around the deltoid battens148 before the sheets of the outer shell layer 186 are applied, in orderto hold the battens 148 to the bushing 40 and the core 62.

Once the winding process of fibrous sheet material 164 and filamentarymaterial 131 around the bushings 40 and core 62 has been completed, thefinal assembly 120 shown in FIG. 12 may then be removed from thebearings 130.

As shown in FIG. 6a , the bushing 40 may have a plug 75 blocking itsinternal bore 109. Optionally, the plug 75 may be positioned between thefrustoconical recess 65 and the bore 109. The plug 75 may prevent matrixmaterial from flowing from the recess 66 into the bore 109 during theinfusion process. Optionally, the plug 75 may be integral with thebushing. Alternatively, the plug may be added as a separate element inthe bore 109.

Each pultruded preform 150 in the assembly 120 may comprises a “dry”fibre material containing binder material but no resin, so it is porousand becomes infused with epoxy resin in the infusion mould. In analternative embodiment, each pultruded preform 150 in the assembly 120may be supplied as a cured fibre-reinforced composite material—such as afibrous material in a cured vinyl ester resin.

After it has been moulded in the mould cavity and cured, theintermediate product shown in FIGS. 17-20 can be removed from theinfusion mould. The intermediate product of FIGS. 17-20 is referred tobelow as a blank 190. The walls 182, 183, 185 of the mould cavity maygive the blank 190 a desired outer profile, an example of which is shownin FIGS. 17-20. It should be noted that in FIGS. 17-20 and throughoutthis specification, the draw angle, that is to say the angle ofconvergence of the side faces 343, 344 of the blank 190, at itsrespective end faces 312 a, 312 b is greatly exaggerated, for clarity.In practice, the deviation from a right-angle may be of the order of onedegree or two degrees or of three degrees, between both side faces 343,344.

The purpose of making inserts 105 by the method of placing two bushings40 at either end of a longitudinal core material 62 to form a spindle167, is to optimise and rationalise the forming process for the inserts105. The process is optimised because it allows two inserts 105 to bemade from a single blank 190, by dividing the double-ended blank 190into two parts, to form two inserts. In other words, a single mouldingor forming process of a blank 190 may be used to make two inserts 105.When using the RTM process to form the blanks 190, a problem arises inthat it is difficult to obtain the optimal shape of the inserts 105 bythis method. It is possible to obtain a rectangular prism by RTMmoulding, although it can be difficult to extract a parallel-sided,moulded prism from its RTM mould without using a removable mould insert,in the form of a removable side wall portion which may be tapered toallow its removal from the mould together with the moulded blank. Themoulded blank may then be released from the removable mould insertoutside the mould. The same technique may be used when moulding partswith undercuts. But using a removable wall portion of a mould createsdifficulties when working with resin infusion techniques, because theresin tends to glue the supposedly removable mould elements together, orto clog up the separable mould elements. In any case, even if aparallel-sided rectangular prism shape were moulded to form adouble-ended blank 190, the inserts 105 generated from such a blankwould need to be machined to a slightly trapezoid shape in order toenable the creation of a circular arrangement of inserts 105 around ablade root, when these inserts 105 are butted-up side by side as in FIG.4. It is possible to mould a prism shape in the form of a trapezoid,whose sloping sides would allow removal from an RTM mould. But if atrapezoid prism is to be divided into two identical inserts 105, thedivision can only be by way of a bisection of the lengthwise extent ofthe blank 190. In the case of root inserts 105, this generates asuboptimal shape for the manufacturing process and for the laid upinserts 105 in a blade root 20. In particular, it is desirable toprovide inserts which exhibit a tapering portion, tapering down in adirection away from the root face of a wind turbine blade. This taperedshape of an insert 105 allows a more gradual load transfer between aninsert 105 and the composite material of the wind turbine blade shell27. The creation of a tapered insert from a double-ended blank 190preferably requires a diagonal cut to be made through the blank 190,dividing the blank 109 into two identical inserts 105. When a blank 190has the shape of a rectangular prism, such a diagonal cut generates twoidentical inserts 105. On the other hand, if the blank has the shape ofa trapezoid, the two inserts 105 generated from a diagonal sectioningcut will be non-identical, as in a left and a right shoe, or such like.This means that when forming a circle from the tapered trapezoid inserts105 arranged side-by-side, one set of inserts will leave the taperedfaces oriented in a direction opposite to the orientation of the taperedfaces of the other set of inserts. In other words, one set of insertswould be unusable. In either case, whether moulding rectangular ortrapezoidal blanks 190, an additional machining step would be requiredto be performed on the sectioned inserts 105 in order to generateinserts 105 which can be fitted together to create a circle of inserts105 having a consistent geometry. In order to overcome this problem, itis suggested to generate the blank 190 in the form of a double trapezoidshape. This double-trapezoid shaped blank 190 allows the creation of twoidentical, tapered inserts 105 each having a slightly trapezoid crosssection, merely by diagonally sectioning the blank 190. Such inserts 105may be laid-up at a root portion 20 of a wind turbine blade 18 withoutfurther machining, and preferably without requiring the insertion ofwedge-shaped shims between adjacent inserts 105. A double-trapezoidblank 190 has an advantageous shape, allowing it to be bisected into twoidentical or near-identical inserts 105. Aspects of the presentinvention may include a process for making such a blank 190, whichprocess is adapted in certain ways, as well as aspects of the blankitself.

FIG. 32 shows a composite, elongate blank 190 having an elongate blankbody 300. The blank body 300 extends longitudinally about a longitudinalaxis (not drawn) between trapezoid end faces 312 a, 312 b. Theillustrated end faces include a first end face 312 a and a second endface 312 b. Each end face 312 a, 312 b is bounded by edges which defineits trapezoid shape. A first end face 312 a comprises two opposingparallel edges: a first, minor end edge 361 a and a second, major endedge 362 a. The first end face 312 a comprises two non-parallel opposingside edges or equal or near-equivalent length: a side, third edge 363 aand a side, fourth edge 364 a. A second end face 312 b comprises twoopposing parallel edges: a major, first end edge 361 b and a minor,second end edge 362 b. The second end face 312 b comprises twonon-parallel opposing side edges: a side, third edge 363 b and a side,fourth edge 364 b. The blank body 300 has four principal, longitudinal,peripheral faces, including a first peripheral face 341, a secondperipheral face 342, a third peripheral face 343 and a fourth peripheralface 344. Each said peripheral face 341-344 extends in a longitudinaldirection of the blank 190. Each said longitudinal face 341-344 connectscorresponding pairs of side edges 361 a and b; 362 a and b; 363 a and b;364 a and b. Said first peripheral face 361, joins a minor, first endedge 361 a with a major second end edge 361 b; said second peripheralface 362, joins a major, first end edge 362 a with a minor, second endedge 362 b; said third peripheral face 363, joins a side, third edge 363a of a first end face 312 a with a side, third edge 363 b of a secondend face 312 b; said fourth peripheral face 364, joins a side, fourthedge 364 a of a first end face 312 a with a side, fourth edge 364 b of asecond end face 312 b. In the embodiment illustrated in FIG. 32, theblank body 300 defines a transition portion of the blank 190, alongwhich the cross section of the blank 190 transitions from a trapezoidshape at a first end 312 a of the transition region to an invertedtrapezoid shape at a second end 312 b of the transition portion 200. Inthe embodiment of FIG. 32, the transition portion 200 extends betweenthe end faces 312 a, 312 b of the blank 190. In other embodiments, atransition portion 200 may begin and end longitudinally inboard of saidend faces 312 a, 312 b, between end portions 192 a, 192 b of the blankbody 300. The first and second peripheral faces 341, 342 of the blank190 may be planar; preferably planar and parallel; preferably also flat.The side, third face 343 and the side, fourth face 344 may bepredominantly, although not strictly planar. The side, third face 343and the side, fourth face 344 may be predominantly planar and slightlycurved or arcuate. Parts of the side faces 343, 344 may be planar. Inparticular, the side faces 343, 344 may comprise more than one planarfacet. The transition portion 200 may have a variable cross sectionalong its length. The transition portion may have a generallyquadrilateral cross section along its length. A cross-section of thetransition portion 200 may include straight, parallel upper and loweredges and non-parallel lateral edges. The lateral edges of across-section across the transition portion 200 may be partly concave orslightly concave. Each end portion 192 a and 192 b may comprise arespective embedded bushing (not shown). The trapezoid cross section ofthe first end portion 192 a is inverted relative to the quadrilateralcross section of the second end portion 192 b. The upper and lower faces341, 342, of the blank body 200 may be parallel and planar trapeziums,which taper in opposite directions. The side faces 343, 344 may benon-planar, continuously curved surfaces which twist along the length ofthe blank. The blank 190 shown in FIG. 32 may be bisected into equalparts, in particular to form two equally dimensioned inserts 105. Abisection plane may pass transversely through the blank 190. Thebisection plane may intersect diagonally with the side faces 343, 344.The bisection plane may intersect at a straight, transverse line withthe upper and lower faces 341, 342. Each insert may extend from a rootface end 232 to an embedment end 236.

In an alternative embodiment, the, and referring to FIGS. 17-23, theblank 190 preferably has the approximate shape of a prism. The blank 190in addition to its transition portion 200 may also comprise a pair ofend portions 192 a and 192 b being a first 192 a and a second 192 brespective end portion. Each end portion 192 a and 192 b may contain arespective bushing 40. Each end portion 192 a or b preferably has fourperipheral faces which meet at four edges or corners to preferably forma slightly trapezoidal cross-section. Thus, for example, the faces ofthe first end portion 192 a may comprise a respective first end portionmajor face 194 a; a first end portion minor face 196 a; and a pair offirst end portion side faces 198 a. On the other hand, the faces of thesecond end portion 192 b may comprise a second end portion major face194 b; a second end portion minor face 196 b; and a pair of second endportion side faces 198 b. Note that the degree of convergence of theangle subtended by the end portion side faces 198 a and 198 b isexaggerated in FIGS. 17-23 to emphasise the trapezoidal shape of thatpart of the blank 190. Preferably all the peripheral faces of the end[portions 192 a, 192 b extend parallel to a longitudinal axis throughsaid blank 190. In embodiments, the opposing, non-parallel side faces198 a, 198 b of the blank 190 near its respective ends, may diverge byan angle of less than five degrees, preferably less than four degrees,preferably three degrees or less.

At a respective first or second end of the blank 190, each said majorface 194 a or b of the blank 190 is wider than its associated minor face196 a or b. As shown most clearly by comparing FIG. 21 with FIG. 23, thetrapezoidal cross section of the first end portion 192 a of the blank190 is inverted relative to the trapezoidal cross section of its secondend portion 192 b. So the major face 194 a of the first end portion 192a (shown in FIG. 23) is at the blank's lower face 342, whereas the majorface 194 b of the second end portion 192 b (shown in FIG. 21) is at itsupper face 341. Similarly the said minor face 196 a of the first endportion 192 a is at the blank's upper face 341, whereas the said minorface 196 b of the second end portion 192 b is at its lower face 342.

In embodiments, a transition portion 200 may extend between the two endportions 192 a,b of the blank 190. As mentioned above, each end portion192 a and 192 b may contain a respective bushing 40 and the trapezoidalcross-section of each end portion 192 a,b preferably does not vary alongthe longitudinal direction of the blank—in other words each end portionhas a parallel-sided prismatic shape. The transition portion 200, on theother hand, has a cross-sectional shape which preferably variescontinuously along the longitudinal direction of the blank. Therefore inthe embodiment of FIGS. 17-23 the transition region 200 defines thatpart of the blank 190 along which there is a shape transition betweenthe mutually inverted trapezoidal cross-sectional shapes of the firstportion 192 a and the second portion 192 b.

The transition portion 200 may comprise a pair of opposing side faces343, 344, each one of which meets a respective end portion side face 198a and 198 b at each of the end portions 192 a and 192 b. One of the sidefaces 343 of the transition portion 200 is shown in FIG. 17, and thecorresponding opposite side face 344 is shown in FIG. 18. Each side face343, 344 of the transition portion 200 of the blank 190 may be smooth,continuous. Alternatively, each said side face may comprise multipleplanar facets. For example a side face 343, 344 of a transition region200 may have two planar triangular facets 202 a,b. According to thisembodiment, top facets 202 b may meet bottom facets 202 a at a diagonaledge or corner 204. The blank 190 of FIG. 17 may be cut into a matchingpair of inserts by cutting along a diagonal edge 204 across a side face343, 344.

The transition portion 200 has a preferably planar upper face 206 bshown from above in FIG. 19 which meets the second end portion majorface 194 b and the first end region minor face 196 a of the end portions192 a, 192 b; and a preferably planar lower face 206 a shown from belowin FIG. 20 which meets the second end portion minor face 196 b and thefirst end portion major face 194 a of the end portions 192 a, 192 b.

FIGS. 21-23 show how the cross-section of the blank 190 may change alongits length. At the mid-point, the cross-section has a waisted profileshown in FIG. 22 with the diagonal edge or corner 204 at a mid-pointbetween the upper surface 206 b and a lower surface 206 a.

An insert 105 shown in FIGS. 24-26 will now be described, using the samereference numbers as the blank 190 from which it may be cut. Theillustrated insert 105 extends from a root face end 232 to an embedmentend 236. It has a root end portion 192 a with faces which form atrapezoidal cross-section, the faces comprising a major face 194 a, aminor face 196 a, and a pair of angled side faces 198 a. The major face194 a is wider than the minor face 196 a. When it is integrated into awind turbine blade 20, the major face 194 a is on the outside of thering of inserts 105, and the minor face 196 a is on the inside. Theinsert 105 also has an extension portion 200 a, formed from the lowerhalf of the transition portion 200 of the blank 190, which tapersinwardly in both height and width as it extends away from the endportion to a pointed tip 224 a. The extension portion 200 a has an outerface 206 a (shown in FIG. 25) which meets the major face 194 a of theend portion; a cut inner face 226 a (FIGS. 24 and 26) which meets theminor face 196 a of the end portion at an edge; and a pair of triangularside faces 202 a. The triangular side faces 202 a may be formed from thelower facets of the side faces 343, 344 of the blank 190. Although theinsert 105 illustrated in FIG. 24 is shown with an end region 192 awhich has all peripheral sides parallel to its longitudinal axis, whichmay also be parallel to a longitudinal axis of a bushing 40 embedded init.

As shown in FIG. 25, the insert 105 may exhibit a maximum widthdimension W1 at its root face end 232, larger than a maximum widthdimension W2 at its embedment end 236. The insert may reduce uniformlyin width from W1 to W2 as it extends away from the root end face 323,towards the embedment end 236, at its tip 224. Alternatively, the outerface 206 a of an extension portion 200 a may have a width which reducesuniformly from W1 to W2 as it extends away from the end portion 192 a tothe tip 224 a.

The insert 105 has a height H1 between its upper and lower faces 341,342. The height H1 at a root face end 232 may progressively reduce tozero at an embedment end 236. In alternative embodiments, as shown inFIG. 26, the height H1 at an end portion 192 a, between outer and innerfaces 206 a, 226 a may reduce uniformly from H1 to zero as it extendsaway from the end portion 192 a to the tip 224 a of the extensionportion 192 a.

As described above with reference to FIG. 4, an insert 220 a may beintegrated into a blade root 20 between glass fibre composite walls 41and 42 with its outer faces 194 a, 206 a bonded to the outer compositewall 41 and its inner faces 196 a, 226 a bonded to the inner compositewall 42. The angle of taper between the outer and inner faces 206 a, 226a of the extension portion of the insert may lie between 2 degrees and20 degrees; preferably between about 2 degrees and 15 degrees;preferably between about 2 degrees and 10 degrees; preferably betweenabout 3 degrees and 10 degrees; preferably between about 4 degrees and 8degrees. In one embodiment, the angle of taper between the outer andinner faces 206 a, 226 a of the extension portion of the insert may beabout arctan(0.1)—i.e., about 6° (note that this angle of taper isexaggerated in FIG. 26). This low angle of taper means that the plies ofthe inner composite wall 42 can be dropped off gradually. This mayresult in a low stress concentration when loads are transferred betweenan insert 220 a and a blade 20. For example, about five or ten or moreplies may be dropped off along the length of the angled inner face 226a.

Preferably, the assembled elements for making a blank 190 may be placedin a resin transfer moulding (RTM) infusion mould, an example of whichis shown in FIG. 16. The illustrated infusion mould 250 may comprise abase 180 with opposing side walls 182, a floor 185, and a lid 181, whichtogether define a mould cavity. The lid 181 may have a moulding topsurface 183 opposite the floor 185. FIG. 16 shows the two parts 180,181of the mould 250 containing an insert assembly 120. After the lid 181 isfitted, a matrix material (such as epoxy resin) is injected into theinfusion mould 250 so that the matrix material infuses though the porousfibrous material forming the transition layer 102, around or through thebattens 148 and the outer shell layer 186. The assembly 120 therebyadopts the profile of the mould cavity. Still with reference FIG. 16:the floor 185 of the base 180 and the moulding surface 183 of the lid181 may contact and mould the side faces 343 and 344 of the blank 190.The side walls 182 of the base may contact and mould its upper face 341(or including 194 a, 206 a, 196 b) and lower face 342 (or including 196a, 206 b, 194 b). Note that the angles of the upper and lower surfaces183,185 may be exaggerated in FIG. 16 for purposes of illustration.

In the finished blank 190, the upper and lower faces 341, 342 may beparallel, in fulfilment of the trapezoidal cross-section of the endportions of a blank 190. However, for moulding the blank in a recessedmould having fixed, opposing side walls 182 and a fixed floor surface185, per FIG. 16, the side walls 182 of the base 180 may need to beformed with a small draw rather than being parallel in order to allowremoval of the moulded blank 190 from the mould base 180. Optionally theblank 190 may then be machined to remove the excess material caused bythe small non-parallel, divergent draw, so that the upper and lowerfaces 343, 344 are made parallel for the cross-sections of the endportions 192 a,b to become precisely trapezoidal.

The four battens 148 may preferably be similar or identical, so theouter profile of the assembly 120 may be square rather than trapezoidalas it is fitted into the infusion mould 180 as shown in FIG. 16.Optionally a twist or plait of glass fibre roving may be placed in thelower corner 188 of the mould base 180 at the wide part of the trapezoidsection, preferably under any sheets of undirectional glass fibre whichmake up the shell 186. Similarly, a twist or plait of glass fibre rovingmay be placed in the upper corner 189 at the wide part of the trapezoidsection. The glass roving may be placed under the one or more sheets ofundirectional glass fibre sheet material which make up the shell 186.These twists/plaits give the assembly 120 a slightly trapezoidal shapeprior to moulding, and encourage greater conformity into the mouldcorners.

Once the blank 190 has been cured and removed from the mould 250, it maybe cut diagonally into two equally dimensioned parts. The provision of ablank 190 with a double-trapezoid shape as described herein, wherein onetrapezoidal end 192 a is inverted in relation to the other trapezoidalend 192 b, ensures that the two inserts 105 which are formed as a resultof bisecting the blank 190 are of equal dimensions and substantiallyidentical. In embodiments, cutting may be carried out along the diagonaledges 204 to provide a matching pair of inserts 105. One of the inserts105 of the matching pair is shown in FIGS. 24-26.

An alternative infusion mould 250 for infusing and shaping the blank 190from an assembly 120 is shown in FIG. 27. The mould 250 comprises firstand second mould parts which meet at a split line 259: namely a base 251and a lid 252. The base 251 has a pair of moulding faces 254, 255 andthe lid 252 has a pair of moulding faces 256, 257.

Unlike the infusion mould of FIG. 16, each mould part 251, 252 contactsand moulds a respective side face 343, 344 of the blank 190. So themoulding face 255 of the base may contact one side face 343, and thediagonally opposite moulding face 256 of the lid may contact the otherside face 344.

By way of example, the lower face 342 of the blank 190 may be contactedby the moulding face 254 of the base 251; and the upper face 341 of theblank 190 may be contacted by the diagonally opposite moulding face 257of the lid 252. The base 251 may thereby mould both the minor face 196 bof the second end portion and the major face 194 a of the first endportion, and the lid 252 may mould the major face 194 b of the secondend portion and the minor face 196 a of the first end portion.

The split line between the base 251 and the lid 252 substantiallycoincides with a diagonal of the quadrilateral cross-section of theblank 190, which is its maximum cross-sectional dimension. This diagonalsplit mould arrangement thereby has an intrinsic draw angle whichenables the cured blank 190 to be removed from the mould in its finalshape—not requiring any machining after it has been removed from themould, unlike the arrangement of FIG. 16. The diagonal split mouldthereby removes a need for additional machining of the blank or insertsbefore use in a blade root 20 lay-up.

The mould cavity of the diagonal split mould 250 of FIG. 27 thereforepreferably has a trapezoid cross-section at each end, so the endportions of the moulded and cured blank 190 have the described trapezoidcross-sections. In a further alternative moulding arrangement, the mouldcavity of the diagonal split mould 250 of FIG. 27 may have a square orrectangular cross-sectional shape rather than double-trapezoid. Themoulded and cured blank may then be then machined to give it thedouble-trapezoid shape shown in FIGS. 17-23 before it is cut diagonallyto provide the matching pair of inserts, although this variant is notpreferred.

FIG. 14 shows a two-batten arrangement in which each batten 148optionally has a pair of lobes. The lobes may be formed from pultrudedfibrous preforms 150 or e.g., formed by glass fibre rods 160. FIGS. 28and 29 show similar lobed batten arrangements formed from pultrudedpreforms 150. According to an embodiment illustrated in FIG. 28, the twopreforms 150 may have first and second lobes joined by a connectionportion. The lobed battens 148 may be arranged on opposite sides of anassembly 120, to make up part of the body 108 of an insert 105. Stillalternatively, as shown in FIG. 29, the two-lobed battens 148, in theform of preforms 150 may be arranged on the top and bottom of theassembly 120. Each lobe preferably has a deltoid cross-section with aconcave inner face which contacts the transition layer 102, and a pairof outer faces 261 which meet at a convex corner 262.

The battens 148 may extend along the full length of a bushing and core62 up to the root end of the bushing 40. FIG. 30 shows an example ofsuch an arrangement. In this case the bushing 40 may have undulationsformed along its full length, unlike in the embodiment of FIG. 6a inwhich the bushing has a root end region 61 with a smooth cylindricalouter surface with no undulations.

It may be desirable to axially separate the functions of, on the onehand, transferring loads between a hub connection bolt and a bushing 40,and on the other hand, transferring loads between a bushing 40 and aninsert body 108. Therefore, it may be desirable to axially offset theposition of a thread 66, or other connection feature inside a bore 109of a bushing 40, from the transition layer 102, which provides anchoringbetween the bushing and the insert body 108. To this end, as discussedthe transition layer 102 may terminate axially inboard of a root endface of a bushing 40. At the same time, a thread 66 or other connectionfeature inside a bore 109 may be positioned at an end region of thebushing 40 axially offset from the transition layer 102. At the sametime, in embodiments, the battens 148 may terminate at the end of thebody region 59 where it meets the end region 61. In particular, thebattens 148 in the body 108 of an insert blank 190 may terminate shortof a root face end 232 of an insert or bushing 40. In this case,one-piece, flexible end caps 310 may be fitted over the end regions 61.The end caps may in particular have the required square or trapezoidalouter profile of the insert body 108. In embodiments, preferably, thetrapezoid cross-section shape of the insert body 108 may have an axis ofsymmetry extending perpendicular to its parallel sides.

An example of such an end cap 310 is shown in FIG. 31. The illustratedend cap 310 may have four corner lobes 312 with the required deltoidcross-section, and a bore with a smooth cylindrical inner surface 311which abuts the smooth cylindrical outer surface of the bushing endregion 61. The end cap 310 may prevents the ingress of water or oil intothe insert body 108.

Preferably, the end cap 310 may be formed from a low modulus plasticmaterial. For example the end cap 310 may be formed from a material witha modulus less than 1 GPa, which is much less than the modulus of thebattens 148 (typically of the order of 40 GPa). The relatively lowmodulus of the end cap 310 ensures a simple stress field with theprimary load path from the internal thread 66 into the battens 148 beingvia the body region 59 and the transition layer 102, and not via the endcap 310. The end cap 310 may optionally be glued in place.

FIG. 33 shows a blank 190 with a further alternative geometry. In theembodiment illustrated in FIG. 33, each triangular facet 202 a,b may runalong only half the length of the transition portion 200 up to avertical edge 205.

The term trapezoid in the present context denotes a quadrilateral shapehaving a pair of parallel sides and a pair of non-parallel sides.

Although the invention has been described above with reference to one ormore preferred embodiments, it will be appreciated that various changesor modifications may be made without departing from the scope of theinvention as defined in the appended claims.

1. A composite material blank comprising an elongate blank bodyextending between a first end face and a second end face; said blankbody extending in a longitudinal direction, parallel to a longitudinalaxis thereof, and having four peripheral side faces; each said first andsecond end face having edges which define a trapezoid shape; wherein theperipheral side faces of said blank body connect the edges of said firstend face with the edges of said second end face; and wherein said firsttrapezoid end face is inverted in relation to said second trapezoid endface.
 2. The blank according to claim 1, said blank body exhibiting twoplanar faces joined by two non-parallel, side faces.
 3. The blankaccording to claim 1, said blank being shaped to generate twoidentically dimensioned parts, when bisected along a plane transverse tothe lengthwise axis of said blank.
 4. The blank according to claim 1,said blank comprising a first and a second wind turbine blade rootbushing wherein said first and second bushings are arranged oriented inopposition to each other.
 5. The blank according to claim 1, said blankbody comprising a first end portion and a second end portion.
 6. Theblank according to claim 4, wherein a said first bushing is arranged insaid first end portion of said blank body, and a said second bushing isarranged in said second end portion of said blank body.
 7. The blankaccording to claim 5, wherein, along the length of said first and secondend portions, the said four peripheral sides of said blank body areplanar and extend parallel to the longitudinal axis of said blank. 8.The blank according to claim 7, said blank further including atransition region in which two said side faces of said blank body arenot parallel to said longitudinal axis.
 9. The blank according to claim2, wherein each said side face comprises two or more substantiallyplanar facets.
 10. The blank according to claim 4, wherein the blankfurther comprises two or more fibrous battens surrounding said bushings,and wherein each batten has a deltoid cross-section, so that the battensgive the blank body a quadrilateral cross-section.
 11. The blankaccording to claim 7, wherein each said end portion has a prismaticshape.
 12. A method of manufacturing a pair of inserts for a windturbine blade root, the method comprising: producing a blank accordingto claim 1; and cutting the blank into two equal pieces by making adiagonal cut through the blank body.
 13. The method of claim 12, saiddiagonal cut defining a plane which passes transversely across opposingparallel faces of said blank body, and which passes diagonally acrossopposing side faces of said blank body.
 14. A method of manufacturingthe blank of claim 1, the method comprising: placing an assembly in aninfusion mould; injecting a matrix material into the infusion mould sothat the matrix material infuses the assembly; curing the matrixmaterial; and after the matrix material has cured, removing the blankfrom the infusion mould.
 15. The method of claim 14, wherein saidinfusion mould comprises first and second mould parts which meet at asplit line, wherein each of said first and second mould parts mouldsrespectively two principal surfaces of said blank, wherein said firstmould part moulds one of two opposing side faces of said blank and oneof two opposing parallel faces of said blank, while said second mouldpart moulds the other of said two opposing side faces of said blank andthe other of said two opposing parallel faces of said blank.